Using transformation mappings in JPQL or Expression queries is not currently directly supported. Please log a bug for this.

You can define a user defined QueryKey using a DescriptorCustomizer to access the columns, but I think JPQL does not support QueryKey's either (please log a bug for that), but you can use Expression queries.

However, you may be better off trying to map the Param object as an Embeddable object in JPA. The you would be able to query it.